The present invention relates to a method and structure for connecting a terminal with a wire in which a tubular wire connecting portion of a terminal is crimp-connected to a core of a wire in a uniform manner over the whole circumference by using, for example, a rotary swaging machine.
Conventionally, a wire is connected to a terminal by the following connecting method. As shown in FIGS. 21A and 14B, for example, a core 37 of a wire 35 is crimped by a pair of crimp pieces 34 which are erected from both sides of a bottom plate 36 of a terminal 33, and the paired crimp pieces 34 are crimpingly deformed into a substantially eyeglasses-like shape, whereby the core 37 is strongly pressed from both the sides and tip ends 34a of the crimp pieces 34 are caused to bite the middle area of the core 37. As a result, the contact between the core 37 and the crimp pieces 34 is attained. As shown in FIG. 21B, inside the crimp pieces 34, the diameter of the core 37 is reduced, and, in the front and rear end sides of the crimp pieces 34, the diameter of the core 37 is outward increased, so that the core 37 is crimped by the wedge function.
The connecting method using the pair of crimp pieces 34 is effective for the wire 35 of a small diameter. By contrast, for a wire of a large diameter such as a shielded wire through which a large current can be flown, the method has a problem in that the contact area between the crimp pieces 34 and the core is small and the electric resistance is easily increased.
Therefore, a terminal of a type in which a core is crimped equally in the circumferential direction is used for such a wire of a large diameter. As an example of a connecting method using such a terminal, FIG. 22 shows a method of connecting a terminal with a wire which is disclosed in Japanese Utility Model Publication No. 43746/1975.
In the connecting method, under a state where a core of a wire is inserted into a tubular wire connecting portion of a terminal, the tubular wire connecting portion is crimped into a hexagonal shape by a pair of upper and lower dies 21, to cause the core 23 to be closely contacted into the wire connecting portion 22. As shown in FIG. 23, each of the dies 21 has three pressing faces 24, and a center ridge 25 is formed on each of the pressing faces 24. As shown in FIG. 22, the ridges 25 radially press the centers of the outer faces of the hexagonal wire connecting portion 22 to enhance the contact performance between the core 23 of the wire and the wire connecting portion 22 of the terminal.
However, the conventional connecting method and the connecting structure using the method have a problem in that, as shown in FIG. 22, burrs 26 are easily produced between the upper and lower dies 21 and on both sides of the wire connecting portion 22, and a large manpower is required for removing the burrs 26. When the wire connecting portion 22 of the terminal is crimped by using the upper and lower dies 21, as shown in FIG. 24, the vertical crimp forces (internal stress) P1 which are directed to the center of the core 23 largely act, and the crimp forces (internal stress) P2 on the lateral portions tend to be reduced, thereby causing another problem in that a gap is easily formed on both sides of the wire connecting portion 22 and between the element wires of the core 23, or between the core 23 and the wire connecting portion 22. When such a gap is formed, the electric resistance is increased to produce the possibilities that the power transmission efficiency is lowered, and that the connecting portion is overheated.
FIG. 25 shows a mode of crimp-connection of a wire by using a method similar to that of FIG. 22. The ridges 25 of the dies 21 (FIG. 23) radially press a core 23′ of a wire at six places as indicated by the arrows F. Therefore, the core 23′ is deformed so as to have a tortoise-like section shape, and stress concentration (the chain lines 29 show the distribution of internal stress) occurs in regions of a wire connecting portion 22′ of a terminal which are between recesses 27 due to the ridges 25 (FIG. 23), i.e., in the vicinities of convex portions 28, and the crimping on the core 23′ becomes uneven in the circumferential direction. As a result, gaps (gaps between element wires) 30 are easily formed in the core 23′, gaps 31 are easily formed also between the core 23′ and the wire connecting portion 22′ of the terminal, and the wire connecting portion 22′ tends to crack because of the stress concentration, thereby producing a problem in that the strength is reduced. When the gaps 30 and 31 are formed, the electric resistance is increased in the same manner as described above to produce the possibilities that the power transmission efficiency is lowered, and that the connecting portion is overheated. Moreover, there is a further possibility that the core 23′ easily slips from the wire connecting portion 22′.